The present invention relates to imaging optic fibers, and in particular to fiber optic cables having a flexible center section and non-flexible end sections held in protective ferrules.
It is known in the art of imaging optic fibers and optic fibers for signal transmission to create a fiber optic bundle by heating and drawing glass fibers which are spaced apart by or encapsulated in leachable spacers in order to form a fused optic fiber bundle. The ends of the optic fiber bundle are masked or protected, and the bundle is then placed in a leaching agent which leaches the leachable spacers from center section of the bundle between the protected ends. This results in the center section being flexible. The bundle is preferably covered with a protective sheath to form a flexible optic fiber cable.
Generally, ferrules or casings are attached to the non-flexible end sections in order to protect the end sections from damage and to allow the end sections to be connected in connectors. This can be done prior to or after leaching. While it is desired that the end sections of the optic fiber bundle be centered within the ferrules, typically, the optic fibers cannot be justified within the ferrule since the optic fibers will settle to the lower side of the ferrule as the adhesive which attaches the end section of the optic fiber bundle to the ferrule cures. While a ferrule having smaller inside dimensions can be utilized, this can lead to problems with the insertion of the end sections of the fiber optic bundle into the ferrule and the destruction of the outside optic fibers of the bundle.
Additionally, for optic fiber bundles made with fiberglass or synthetic fibers, the ferrules have typically been crimped onto the outside of the ends of the fiber optic bundle. Since the diameter of the optic fiber bundle may vary widely based upon the size of the fibers and variations in production conditions, the crimping of the ferrule onto the bundle often leads to a connection that is either too loose if the diameter of the bundle is small, or to damage or destruction of the outer fibers, if the diameter of the bundle is too large.
It would be desirable to provide a flexible fiber optic cable and a process for producing such a cable that has the advantage of not compressing the ferrule on the end section of the optic fiber bundle, and which allows for a centering of the end sections of the optic fiber bundle in the ferrules. It would also be desirable to provide an optic fiber cable assembly and a process for assembling such a cable which would result in less damage to the fibers of the end sections in the cable.
Briefly stated, the present invention provides a flexible optic fiber cable having a plurality of optic fibers grouped together as a fiber bundle with a flexible center section, in which the optic fibers are moveable relative to adjacent fibers in the fiber bundle, and two non-flexible end sections, in which the plurality of optic fibers are joined together in a predetermined arrangement. Each of the two non-flexible end sections includes a generally uniform thickness protective layer extending over an outer surface thereof starting at a position spaced inwardly from a free end of the end section. A ferrule is located around and in an interference fit with the protective layer so that the end section is centered in the ferrule. An adhesive is located between the ferrule and the non-flexible end section from the position spaced inwardly from the free end of the end section to the free end thereof to connect the ferrule to the non-flexible end section.
In another aspect, the invention provides a method of manufacturing an optic fiber cable having a flexible center section and two non-flexible end sections. The method includes the steps of:
coating each of the end sections with a generally uniform protective layer;
removing a portion of the protective layer from each of the end sections from a position spaced inwardly from a free end of each of the end sections to the respective free ends thereof;
inserting each end section into a ferrule that has an interference fit with the protective layer, centering the end section in the respective ferrule; and
adhering each of the ferrules to the respective end sections with an adhesive located between each of the ferrules and the respective end sections from the position spaced inwardly from the free end of each of the respective end sections to the respective free ends thereof.